netdev - RE: [RFC NET 00/02]: Secondary unicast address support

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Date:	Thu, 21 Jun 2007 14:11:49 -0700
From:	"Caitlin Bestler" <caitlinb@...adcom.com>
To:	netdev@...r.kernel.org
Subject: RE: [RFC NET 00/02]: Secondary unicast address support

netdev-owner@...r.kernel.org wrote:
> From: ebiederm@...ssion.com (Eric W. Biederman)
> Date: Thu, 21 Jun 2007 13:08:12 -0600
> 
>> However this just seems to allow a card to decode multiple mac
>> addresses which in some oddball load balancing configurations may
>> actually be useful, but it seems fairly limited.
>> 
>> Do you have a specific use case you envision for this multiple mac
>> functionality?
> 
> Virtualization.
> 
> If you can't tell the ethernet card that more than 1 MAC
> address are for it, you have to turn the thing into promiscuous mode.
> 
> Networking on virtualization is typically done by giving each
> guest a unique MAC address, the guests have a virtual network
> device that connects to the control node (or dom0 in Xen
> parlace) and/or other guests.
> 
> The control node has a switch that routes the packets from
> the guests either to other guests or out the real ethernet interface.
> 
> Each guest gets a unique MAC so that the switch can know
> which guest an incoming packet is for.

The same software switch could also throw away the excess
frames that promiscuous mode would have admitted. Unless
the misdirected frames were common it would not seem to 
be a major CPU burden.

Keep in mind that the only MAC addresses that would have
been transmitted are the ones that the input filter would
have listed. 


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